\documentclass{article}

\usepackage{siunitx,multirow,booktabs}

\begin{document}
\begin{table}[h!]
	\caption{Change of amplitude of the waveform at peak A during the transition from baseline to venous occlusion.}
	\label{tbl:change_A_venous}
	\centering\smallskip\small
	\begin{tabular}{l
		*{3}{S[table-format=1.4]@{\,\( \pm
		\)\,}S[table-format=1.4]} %Format for Z+-std
		cc}
		\toprule
		              & \multicolumn{2}{c}{\multirow{2}{*}{\textbf{Baseline [\si{\ohm}]}}}
		              & \multicolumn{2}{c}{\multirow{2}{*}{\textbf{Occlusion [\si{\ohm}]}}}
		              & \multicolumn{2}{c}{\multirow{2}{*}{\textbf{Baseline [\si{\ohm}]}}}
		              & \multicolumn{2}{c}{\textbf{Change [\%]}}                                                                                                   \\
		              & \multicolumn{2}{c}{}
		              & \multicolumn{2}{c}{}
		              & \multicolumn{2}{c}{}
		              & \textbf{R1-R2}                                                      & \textbf{R2-R3}                                                       \\\midrule
		Participant 1 & 0.0283                                                              & 0.0233         & 0.0342 & 0.0191 & 0.0305 & 0.0305 & 20.93  & -13.29 \\
		Participant 2 & 0.0491                                                              & 0.0102         & 0.0595 & 0.0140 & 0.0449 & 0.0449 & 21.01  & -29.68 \\
		Participant 3 & 0.0346                                                              & 0.0351         & 0.0374 & 0.0144 & 0.0294 & 0.0294 & 7.91   & -22.89 \\
		Participant 4 & 0.0252                                                              & 0.0303         & 0.0272 & 0.0139 & 0.0222 & 0.0222 & 7.98   & -19.87 \\
		Participant 5 & 0.0345                                                              & 0.0112         & 0.0481 & 0.0098 & 0.0376 & 0.0376 & 39.68  & -30.69 \\
		Participant 6 & 0.0233                                                              & 0.0105         & 0.0306 & 0.0124 & 0.0251 & 0.0251 & 31.33  & -23.52 \\
		Participant 7 & 0.0359                                                              & 0.0080         & 0.0537 & 0.0081 & 0.0365 & 0.0365 & 49.72  & -47.78 \\
		Participant 8 & 0.0237                                                              & 0.0094         & 0.0211 & 0.0091 & 0.0127 & 0.0127 & -11.11 & -35.30 \\  \bottomrule
	\end{tabular}
\end{table}
\end{document}


